Boomstacker (UND-049) - Unsanctioned

As Boomstacker enters the battlefield and whenever it attacks, stack two dice on top of it. (All dice must be stacked vertically, one on top of another.)
Boomstacker gets +1/+1 for each die in its stack.
Boomstacker attacks each combat if able.
When the stack falls, sacrifice Boomstacker.